Did you go to the stormcloak camp and listen to Galmar? Can you then follow him to the bridge and lower it? And after you lower it and go into Whiterun is it business usual? no attack? Because during the attack all the NPC are in their homes with the doors locked. Some of the paths are blocked and there should be catapults shooting back at the cloaks outside. Galmar and Ralof should map in with you. Have you gone into Dragonsreach and confronted Balgruuf? Or is he just sitting on his thone?
When you start the quest, Whiterun is not even a place you can fast travel too. If you go back to Ulfric is Whiterun on your map to fast travel too?